New BNG Rules and Exemptions Apply from 6th August 2026

The new Biodiversity Net Gain (BNG) rules applying from the 6th of August 2026 introduce important changes for developers, planning teams, landowners and consultants. These updates affect which developments may be exempt from mandatory Biodiversity Net Gain and which projects will still need to meet the biodiversity gain condition.

At first glance, the new BNG exemptions may appear to reduce the burden for smaller or temporary developments. However, there is an important caveat: where onsite priority habitat is negatively impacted, several exemptions will not apply. This means developers should not assume that a small site, temporary permission or limited habitat impact automatically removes the need to consider BNG.

What are the new BNG rules from 6 August 2026?

The Government has confirmed several updates to BNG exemptions, including a new exemption based on certain areas, a temporary development exemption, changes to self-build and custom build exemptions, and specific exemptions for offsite gain developments.

The most significant change is the new exemption for developments where the site area within the red line boundary is 0.2 hectares or below. This is designed to reduce mandatory BNG requirements for the smallest developments. However, this exemption does not apply where the development negatively impacts onsite priority habitat.

Temporary developments will also be exempt from BNG from 6 August 2026, provided the whole development is temporary and planning permission is granted for five years or less. Again, this exemption will not apply if onsite priority habitat is negatively affected.

The Government has also confirmed that developments creating or enhancing habitats solely or mainly to fulfil the BNG planning condition for another development will be exempt. This is because these sites are acting as gain sites, providing biodiversity units to offset the impacts of a separate development.

One further change is that the self-build and custom build exemption will no longer apply to new planning applications submitted after 6 August 2026. This is an important update for individuals, developers and planning teams who may have previously expected self-build or custom build schemes to fall outside mandatory BNG.

Which Biodiversity Net Gain exemptions are most relevant?

The new BNG rules mean developers need to look carefully at the type, scale and ecological context of a project before deciding whether BNG applies. The table below summarises the key position from 6 August 2026.

These Biodiversity Net Gain exemptions should be interpreted carefully, particularly where a site contains, or may contain, priority habitat. A development impacts a habitat where it decreases its biodiversity value, so early ecological review remains important even where the site appears small or temporary.

What has stayed the same?

The Government has reiterated the de minimis exemption. BNG does not apply to developments that impact less than 25 square metres of onsite habitat within the red line boundary, and less than five metres of onsite linear habitat such as hedgerows.

This small-impact exemption remains part of the BNG rules, but it should not be treated as a shortcut. If priority habitat is affected, the exemption will not apply and BNG must be met. Developers should therefore be careful when assessing whether works genuinely fall below the de minimis threshold and whether any onsite habitat has priority status.

Some existing exemptions also remain in place. Developments that are part of, or ancillary to, the high-speed railway transport network continue to be exempt. Urgent Crown developments and developments granted planning permission by a development order, including permitted development rights, are also exempt under the Environment Act 2021.

Why is the priority habitat caveat important?

The priority habitat caveat is one of the most important parts of the new BNG rules. It means that certain Biodiversity Net Gain exemptions are not available where onsite priority habitat is negatively impacted, including the new 0.2 hectare exemption, the de minimis exemption and the temporary development exemption.

This is significant because some developers may assume that a small site automatically falls outside BNG. In practice, the ecological value of the site still matters. A small development that affects priority habitat may still need to meet mandatory BNG, even if it falls within the 0.2 hectare threshold.

For planning and development teams, this makes early site assessment particularly important. Before relying on an exemption, organisations should establish what habitats are present, whether any are priority habitats, and whether the proposed development would reduce their biodiversity value.

What do the new BNG rules mean for developers?

The new Biodiversity Net Gain exemptions may remove BNG requirements for some small and temporary developments, but they also create a need for careful screening. The risk is that developers assume an exemption applies, only to discover later that onsite habitat conditions, planning requirements or application timing change the position.

Developers should consider the following practical steps:

• confirm the size of the site within the red line boundary;

• assess whether there are priority habitats on site and level of impact

• confirm whether the development is temporary and limited to five years or less;

• review the applicability of exemption categories

• document the reasoning behind any exemption claim.

This does not mean every small site requires a complex ecological assessment. It does mean that assumptions should be avoided. A proportionate review at the start of a project can reduce the risk of delays, redesign, additional reporting or later planning issues.

What is still expected?

Further announcements on BNG are still expected, so developers should continue to monitor official guidance. The Government has already indicated that amendments and transitional arrangements are part of wider work to improve the implementation of BNG for minor, medium and brownfield development.

This means the practical application of BNG rules may continue to evolve. Organisations involved in planning, development or land management should make sure internal processes are updated as guidance changes. This is especially important where project pipelines include small sites, temporary developments, self-build schemes or offsite biodiversity gain sites.

The bottom line

The new BNG rules applying from the 6^th of August 2026 introduce important Biodiversity Net Gain exemptions for small and temporary developments, while removing the self-build and custom build exemption for new planning applications. However, the exemptions are not automatic in all cases. Where onsite priority habitat is negatively impacted, BNG may still apply.

For developers, the key message is to screen early, document decisions and avoid assuming that site size alone determines whether BNG is required. A clear understanding of habitat impact, priority habitat status and application timing will help reduce planning risk and ensure projects remain aligned with current BNG requirements.

Tunley Environmental supports organisations with biodiversity, nature and regulatory compliance services. Our scientists can help businesses and developers understand BNG rules, assess habitat impacts and prepare for changing biodiversity expectations.